1. Field of the Invention
The present invention is generally related to wireless communication systems and method for the same, more particularly, to wireless communication systems for achieving improved backoff control after network nodes detect collisions on the shared medium.
2. Description of the Related Art
The IEEE 802.11 specification is one of the recommended international standards for WLANs (Wireless Local Area Network). The specification contains technical details for the Medium Access Control (MAC) layer and the Physical (PHY) layer of the communication protocol.
Priority control of communications over the IEEE 802.11 WLANs is one of the issues. Japanese Open Laid Patent Application No. 2002-314546A, and its corresponding U.S. patent application No. US2002/0159418 A1 disclose a priority control method for WLANs, which entitles stations requesting high QoSs (quality of service) to enter a prioritized poling list, and thereby provides improved QoS control.
Japanese Open Laid Patent Application No. P2002-252620 discloses another priority control method for WLANs, which provides each mobile station with a list in which available access points are listed with order of priority, and thereby achieves optimized access point selection. Japanese Open Laid Patent Application No. P2001-308866A discloses similar priority control method for WLANs, which is based on the access point list; the access point selection in this priority control method is additionally responsive to the electric field strengths of the responses received from the access points.
Japanese Open Laid Patent Application No. 2000-115842 discloses a priority control method for digital codeless phone system for selecting trunk interfaces. In this system, mobile stations are grouped into a plurality of groups, and preferred trunk interfaces are defined for each group. The trunk interface associated with the group to which a specific mobile station interfaces incoming and outgoing calls for the specific mobile station.
Due to an increased need for providing IP (internet protocol) phone services, including video phone services, recent requirements for WLANs include transmission of real-time audio and video data; however, the communication protocol currently defined in the IEEE 802.11, which is based on the CSMA/CA (carrier sense multiple access with collision avoidance) protocol, suffers from delay in transmission of real-time data. This mainly results from the fact that the backoff control after collision detection currently defined in the IEEE 802.11 specification is not suitable for transmission of real-time data.
Therefore, there is a need for providing an improved backoff control for wireless communication systems, especially for WLANs.